A probabilistic assessment of the effect of post-weld treatment on the fatigue performance of tubular truss bridges

In the design of tubular truss bridges, engineers have found the fatigue performance of the joints to be a critical aspect. In looking for ways to improve this performance, the use of residual stress-based post-weld treatments has been suggested. Although these treatments have been shown to increase the average fatigue lives of welded details under constant amplitude loading conditions in a number of studies, concerns exist regarding their reliability, in particular under realistic, variable amplitude loading conditions. With this in mind, the effect of post-weld treatment on the fatigue performance of tubular truss bridges is assessed herein using a previously developed probabilistic, fracture mechanics-based model, modified to analyze entire bridge structures under realistic, variable amplitude loading conditions. This model uses a systems reliability approach to consider the influences of the various potential crack sites on the overall reliability of the bridge. By analyzing several variants of a typical tubular truss bridge, it is shown that post-weld treatment can result in a significant fatigue performance improvement for this bridge type. This improvement is quantified herein in terms of either a savings in steel weight or an increase in fatigue life. Several additional studies examine the sensitivity of the results of this assessment to variations in the treatment coverage, intensity, and uniformity. These studies show that similar results can be obtained with a partial treatment strategy to those observed when the entire bridge is treated, and that the treatment benefit depends more on the intensity than the uniformity of the treatment.